What's going on here?

I was correcting EKG's when I hit upon this one. From the room number
(not shown), I knew this was a post-open-heart surgery case (the word "Tape" refers to the fact that the patient had tape over part of the chest). These patients often have temporary pacemakers, but that didn't seem to explain
things adequately. Note that the tracings, from top to bottom, are simultaneous.

Want a hint?

Keep scrolling down ....

Hint

If you look at the rhythm strip near the bottom of the tracing, by matching
the complexes in "V1" to those above and below it, you can figure
out which is the QRS. Also, you can figure out that the rounded, positive
deflection in that lead is a T-wave (not a P-wave, as it might first appear).
That leaves you with the spike. Tempting to call it a pacer spike, but
why is one spike in the rhythm strip early, and why don't we see spikes
in any other leads? Yes, why is it that only V1 is so bizarre?

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Solution

I figured it out as far as described above, and then got up and went
to the recovery room for the rest of the answer. Turns out the patient,
a 50 year old man, had a tachycardia that was hard to diagnose. So an EKG
machine was hooked up and V1 was connected to a temporary atrial wire,
thus obtaining an "atrial electrogram". What you are seeing in
V1 is an EKG recorded from inside the atrium, which is why the "p-wave"
looks like a sharp spike, larger than the QRS-T complex! This was thus
a supraventricular (in fact sinus) tachycardia. The early spike, which
made me think that we weren't just dealing with an atrial pacemaker, was
in fact an atrial premature contraction.